Sampling valves for use in high-speed liquid chromatography today generally comprise a stator having a sample injection passage and a solution flow passage, and another stator having a solution flow passage and a discharge passage. These stators are fixed to an axis. Between these stators a rotor is rotatably mounted, which is provided with a sample loop and a sample holding bore through which a solvent is normally made to flow. In order to perform analysis the sample is injected into said sample loop by means of a microsyringe, for example, and then the rotor is rotated to connect the sample loop holding the sample to the line of a solvent reservoir, a solvent feeding pump, and a column. The sample is thus introduced into the column.
When it is required to inject a desired amount of the sample, a microsyringe is normally used to meter the sample and to inject it into a part of the sample loop. The use of the microsyringe is advantageous in that it makes it possible to use all of the available amount of the sample. Errors in the metering with the microsyringe however will adversely affect the reproducibility.